A measured approach
May 1st 2008

High fuel prices are threatening the competitiveness of UK-based businesses. But if companies want to make a real reduction in the amount of steam and hot water they use, the first thing they must do is measure it, says Mark Allinson of ABB

Arecent survey by the Engineering Employers' Federation (EEF) says that continuing fuel price escalation is now posing a real threat to the competitiveness of UK industry. According to the EEF, 93% of the companies surveyed had experienced an increase in energy prices over the last 12 months, with average weighted increases in gas and electricity of 47% and 34% respectively. These rates are more than double the level of increases reported in 2004. In addition, three quarters of companies saw the cost of gas increase in excess of 30%, whilst 40% of electricity consumers saw increases greater than 30%.

As a result, large industrial users in the UK currently face the highest gas prices and some of the highest electricity prices in Europe. This is despite the fact the UK has a fully liberalised gas market and remains the largest producer of gas in the EU.

Worse still, companies see no halt to the increases, with 80% expecting the cost of energy to rise even further in the next year.

The survey highlights that companies are responding to these increases in a number of ways, in particular by looking at how they buy energy and by pressing ahead with energy efficiency measures.

There is help out there. The Carbon Trust (the company set up by the government to help meet its emissions targets) offers lots of advice and stresses that companies need to use a range of techniques to identify and implement both energy and cost-reduction measures efficiently.

Basic common sense housekeeping can help to achieve many low-cost savings, which can add up to 5% or more of an industrial energy bill, while more structured and formal energy management can achieve savings of 20 to 30% or more, depending on which industrial sector a company operates in.

Measure it to manage it But however sophisticated your planned energy management strategy might be, it starts with one essential realisation – you can't manage what you can't measure. The steam and hot water that most companies use to provide process and space heating have to be monitored closely.

This will allow companies to see which parts of their operation are incurring the biggest energy costs. Being able to pinpoint exactly who is using what enables managers to adopt far more sophisticated accounting procedures and encourages operators to take more responsibility for energy usage in their own areas. It also helps to spot problems, such as leaks or malfunctioning equipment, which could be haemorrhaging cash if the trouble is allowed to continue until the next maintenance survey.

Mass appeal Accurate metering is the key. But it's not the volume of steam that's the critical measure of the amount of energy moving around the system. What you really need to know is the mass.

Traditional differential pressure meters such as orifice plates require peripheral paraphernalia including line pressure transmitters, temperature sensors and a flow computer to produce mass readings for steam, all of which adds up to a highmaintenance headache.

Vortex and swirl meters provide a superior alternative, with virtually zero maintenance requirements and greater accuracy – especially in applications where the flow varies over a significant range. Rather than an accuracy of two percent of the upper flow range, which is the best an orifice plate can provide, vortex and swirl meters offer an accuracy class as good as +/-0.5% of reading over the entire flow range. Furthermore, the turndown is up to ten times greater than that of an orifice plate.

Ready, eddy, go So how do they work? Eddies or 'vortices' form in the wake of any obstruction as a fluid flows around it. Vortex meters measure the frequency of the eddies that result when a fluid passes a geometrically defined obstruction called a shedder.

Swirl meters instead rely on static veins at the entrance to the meter to force the fluid into rotation. The meter then measures the frequency of a helical secondary rotation that automatically develops within this pattern.

The frequency of the vortex street in a vortex meter and of the secondary rotation in a swirl meter are each directly proportional to the volumetric flowrate of the fluid, without any need to compensate for changes in pressure, temperature or density. The meters only need to know the temperature of the steam to calculate the mass flow.

Where companies are looking to retrofit meters on existing steam systems, swirl meters offer the added advantage of being able to fit almost anywhere. Most flowmeters need to receive undisturbed flow to deliver accurate results. So they need to be positioned a good distance downstream from pipe bends, valves or other components that might interfere with the readings. Instead of requiring straight inlet and outlet runs of up to 50 pipe diameters and 10 pipe diameters respectively after a modulating valve, which is typical of vortex meters, swirl meters need just three and two diameters in most applications.

This is possible because the rotating flow pattern inside a swirl meter is specially set up by a series of blades at the inlet to the meter and 'deswirled' again at the outlet. This effectively isolates the flow pattern inside the meter from many of the disturbing influences that can cause inaccurate readings in other designs.

Face the facts Having access to proper information about the steam and hot water flows around a site is a tremendously powerful tool for monitoring and controlling energy use.

Strategically positioned meters form the front line in energy management systems, feeding vital information to measurement computers such as the Sensycal from ABB. In today's tough climate of high energy costs, UK companies will find it increasingly difficult to ignore this issue if they want to remain competitive.

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